Boxlang Application Descriptor

BoxLang Application Descriptor

Overview

Application.bx is BoxLang's application descriptor. It defines application-level settings and lifecycle callbacks, and it is the cornerstone for running multiple isolated applications in one BoxLang server/runtime.

Use this skill whenever the question involves:

• app bootstrapping and lifecycle events
• per-app configuration in this.*
• nested apps and scope isolation
• app-scoped schedulers and watchers
• differences between runtime config (boxlang.json) and app config (Application.bx)

Core Model

• BoxLang searches upward from the executing template/script location for the nearest Application.bx.
• Application.bx is instantiated per request/execution context.
• The application scope is persistent for that app name and survives across requests until timeout/stop.
• Multiple unique app names create separate virtual applications in the same JVM.

Multi-Application Isolation

Each unique this.name maps to a unique application memory space:

• isolated application scope
• isolated session tracking/cache namespace
• isolated app-level settings and listener behavior

This enables running multiple apps side-by-side (public site, admin site, API site) in a single server process.

App Name Rules

class {
    this.name = "MyApp"
}

Best practices:

• Always set this.name explicitly.
• Use stable names across deployments unless you intentionally want a new app memory space.
• Avoid dynamic names unless you fully understand memory and lifecycle impact.

If no name is provided, runtime may auto-generate one from the descriptor path for class listeners, which is usually not what you want in production.

Lifecycle Callbacks

Primary callbacks in Application.bx:

• onApplicationStart()
• onApplicationEnd( applicationScope )
• onSessionStart()
• onSessionEnd( sessionScope, applicationScope )
• onRequestStart( targetPage )
• onRequest( targetPage )
• onRequestEnd()
• onError( exception, eventName )
• onMissingTemplate( targetPage )
• onAbort( targetPage )
• onClassRequest( className, method, args )

class {

    this.name = "MyApp"
    this.sessionManagement = true

    function onApplicationStart() {
        application.bootedAt = now()
        return true
    }

    function onRequestStart( string targetPage ) {
        request.started = getTickCount()
        return true
    }

    function onError( any exception, string eventName ) {
        writeLog( text: "Error in #eventName#: #exception.message#", type: "Error" )
        return true
    }

}

Pseudo-Constructor Settings

Common this.* settings in Application.bx include:

• identity and timing: this.name, this.applicationTimeout, this.timezone, this.locale
• sessions: this.sessionManagement, this.sessionTimeout, this.sessionStorage
• data and cache: this.datasource, this.datasources, this.caches
• loading and resolution: this.mappings, this.classPaths, this.javaSettings
• app async wiring: this.schedulers, this.watchers

App-Scoped Schedulers and Watchers

Application.bx can wire async infrastructure per app:

class {

    this.name = "MyApp"

    this.schedulers = [
        "schedulers.DailyMaintenance",
        "schedulers.HourlyReports"
    ]

    this.watchers = {
        sourceWatcher : {
            paths : [ expandPath( "./src" ) ],
            listener : "app.listeners.HotReloadListener",
            recursive : true,
            debounce : 250,
            atomicWrites : true,
            errorThreshold : 10
        }
    }

}

For deeper async details, see:

• scheduled-tasks
• file-watchers

Runtime vs Application Configuration

• Use boxlang.json for runtime-wide defaults and infrastructure settings.
• Use Application.bx for app-specific behavior and overrides.

Rule of thumb:

• global and environment policy -> boxlang.json
• app identity, lifecycle, and request logic -> Application.bx

Troubleshooting

• Wrong app behavior: verify which Application.bx is being discovered by directory traversal.
• Missing session hooks: verify this.sessionManagement = true and web runtime context.
• Recreated app state: check this.applicationTimeout and applicationStop() usage.
• Async registration not happening: verify this.schedulers / this.watchers values and listener/class paths.
• Mapping/classpath issues: verify paths are relative to the descriptor location and resolve as expected.